Method and apparatus for automatic cleaning of coffee roasters

ABSTRACT

The presence of oils, tars, steam and chaff in the recirculating gases of high-velocity, low-temperature coffee roasters requires frequent shut-downs for mechanical cleaning purposes. With associated cooling-off and heating-up periods, the production loss is significant. The present invention provides means for periodically cutting off the flow of beans to the roaster and heating the gas recirculation portions to the ignition temperature of the deposited by-products (a temperature of from about 500* to 800*F., depending on whether the by-products are light and fluffy or baked on like varnish). After combustion is complete, proper roasting temperatures and atmospheres are restored, and roasting is recommenced. In addition to minimizing down time, the invention more effectively cleans the roaster and prolongs equipment life by reducing metal fatigue resulting from thermal cycling.

iluite States Patent [191 Angstadt METHOD AND APPARATUS FOR AUTOMATICCLEANING OF COFFEE ROASTERS 11 3,733,372 1 May15,1973

Prima y Examinerlohn .l. Camby Atlorney Marn & J angarathis [5 7]ABSTRACT The presence of oils, tars, steam and chaff in therecirculating gases of high-velocity, low-temperature coffee roastersrequires frequent shut-downs for mechanical cleaning purposes. Withassociated cooling-off and heating-up periods, the production loss issignificant. The present invention provides means for periodicallycutting off the flow of beans to the roaster and heating the gasrecirculation portions to the ignition temperature of the depositedby-products (a temperature of from about 500 to 800F., depending onwhether the by-products are light and fluffy or baked on like varnish).After combustion is complete, proper roasting temperatures andatmospheres are restored, and roasting is recommenced. In addition tominimizing down time, the invention more effectively cleans the roasterand prolongs equipment life by reducing metal fatigue resulting fromthermal cycling.

3 Claims, 3 Drawing Figures F RM-[1mm I 3,733,172

sum 1 OF 2 Fig. I.

, John W. Angstodt A TCRNEYS METHOD AND APPARATUS FOR AUTOMATIC CLEANINGOF COFFEE ROASTERS BACKGROUND OF THE INVENTION This invention relatesgenerally to coffee roasting machines and, more particularly, to coffeeroasters wherein heat is transferred to the coffee beans by means of aheated, high-velocity gas stream. Such roasters are in common use today.Of course, it will be appreciated that the invention is applicable toroasting cocoa beans, peanuts and other bean-like materials, however, inthe interest of clarity the invention will be described with referenceto roasting coffee beans. Generally speaking, a burner combusts asuitable fuel in air to provide a hot gas stream at a temperature in therange of 600 to 1200F., usually 600 to 800F. This is introduced into aperforated rotating chamber or kiln containing the coffee beans.Agitation of the beans by lifters or vanes positioned within the chamberprovides for substantially uniform heat transfers to the beans. Afterthe beans reach a predetermined temperature, water sprays meter acontrolled volume of water on them, stopping development at the desiredcolor and restoring moisture lost during roasting. Excess steam escapesthrough the vent pipe. The roasting process is dependent, of course, onboth time and temperatures. However, to minimize the loss of aromaticoils and preserve the glossy finish on the beans, lower temperatures arepreferred. To roast the beans at low temperatures in a reasonable time,i.e., for high production capacity, sensible heat must be transferred tothe beans as quickly as possible. For this reason, high velocity gasstreams are preferred. Typically, air will be at 800F. at 'the beginningof a roast and about 1200F. at completion as it is introduced into theroaster. Exhaust gas temperatures will vary between 200 and 400F. overthe same period, and enters the recirculation system. Production canvary between 2,000 and 6,000 pounds per hour, depending on the size ofthe roaster and type of roast desired.

The coffee fruit comprises a pericarp surrounding the central albumin orgrain, but separated therefrom by the silver skin or tegument. Thepericarp comprises three distinct layers: an outer exocarp, anintermediate mesocarp and an interior endocarp or parchment. Theparchment and silver skin are substantially similar and are oftenconsidered together. Prior to roasting, the pericarp is removed,although a'certain amount of the parchment layer, and the silver skin,are retained. During roasting, water vapor is driven out of the bean,and the bean swells. The combination of dehydration, swelling and theagitation accompanying roasting, causes the silver skin (and/orparchment) to lose its structural integrity, flaking off the bean andforming dust and chaff. This material lodges in the perforations of theroaster or is suspended in the recirculating gas stream.

Oils, tars, and waxes are also evolved from the bean during roasting.Thus, during the course of the roasting operation, the gas stream picksup a variety of byproducts, both gaseous and particulate.

The gases leaving the roaster are passed through a cyclone or othersuitable solids separator wherein particulate material is removed fromthe gaseous stream. Unfortunately, oils and tars are condensed on theinside of the recirculation system. The latter condensates, being tacky,will mechanically hold dust and chaff particles.

Residues also build up in the roaster chamber, clogging the perforationstherein. Consequently, frequent shutdowns for cleaning are necessitatedto maintain operating efficiency and avoid fire risks.

This problem has become more serious in recent years, as coffeeproducers, for economic reasons, have turned to lower-grade coffeebeans. Such lower-grade coffee beans produce a significantly largerpercentage of by-products during roasting thereby magnifying thecleaning problem.

While there are many patents and literature references to the design andoperation of coffee roasters and like devices, these references aredevoid of discussions relating to maintenance of the machines. However,U.S. Pat. No. 1,991,190 of Backer et al is of interest, in that itdescribes the high-velocity low temperature type of roaster used in thepresent invention.

OBJECTS OF THE INVENTION It is a general object of the invention toprovide a process and apparatus for periodically cleaning coffeeroasters.

A further object of the invention is to provide a safe method ofperiodically removing by-products from coffee roaster gas recirculationsystems by controlled combustion thereof.

A further object of the invention is to provide a safe method ofperiodically removing by-products from coffee roaster gas recirculationsystems which requires less time and is more efficient than manualmethods, and which prolongs equipment life.

A still further object of the invention is to provide apparatus which,when installed on a coffee roaster having a gas recirculation system,will carry out the foregoing objects on an automatic or semi-automaticbasis.

Various other objects and advantages of the invention will become clearfrom the foregoing detailed description of an embodiment thereof, andthe novel features will be particularly pointed out in connection withthe appended claims.

THE DRAWING Understanding of the invention will be facilitated byreferring to the accompanying drawings, wherein:

FIG. 1 is a simplified schematic diagram of a low temperature,high-velocity coffee roaster;

FIG. 2 is a schematic diagram similar to FIG. 1 and showing a blockform, greatly simplified, the ordinary control circuitry plus that ofthe invention; and

FIG. 3 illustrates typical circuitry for carrying out the invention.

DESCRIPTION In essence, the present invention comprises raising thetemperature of the air in an empty roaster to within .the range of 500to 800F. for a period of up to 15 minutes. Frequency of clean-out willvary, but once per 24 hours of operation has been found satisfactory inmany of the beans. Inside the roaster 10, there is provided aperforated, rotatable roaster cylinder 16, generally indicated by dottedlines. Spent roaster gases pass through cylinder 16 and exit roasterfrom a gas discharge outlet 17 formed on the bottom of roaster 10. Atemperature sensor T in roaster 10, monitors incoming gas temperature,and modulates the gas supply to prevent overheating of roaster cylinder16. Sensor T near outlet 17, is connected to a high-temperature limitswitch. Temperature sensor T indicates when the recirculation system hasbeen brought to clean-out temperature and starts the clean-out cycletimer, as more fully explained below. A fourth sensor, T was located inthe last portion of the recirculation system to reach clean-outtemperature for test purposes only, and would not ordinarily berequired. A separate thermocouple TC inside the roaster cylinder sensestemperature of the beans.

Discharge chute 14 passes the roasted beans to suitable coolers (notshown).

Hot gases are supplied to roaster 10 by means of a gas introduced intoburner 18, which gas is burned in the presence of air supplied by an airconduit in a muffle 22. The hot combustion gases are passed from muffle22 to roaster 10 via conduit 24, entering the roaster 10 at the endthereof opposite to the charge and discharge chutes. Air supply conduit20 is provided with a movable damper 26 to proportion selectively, asdesired, the quantity of gas in recirculating gas conduit 28 admixedwith air in fresh air conduit 30. A temperature sensor T is located inconduit 28 to monitor the temperature of the exhaust gas.

The gas recirculation system comprises conduits (not shown) connectinggas outlet 17 with recirculation fan 32, connecting the recirculationfan 32 with solids collector cyclone 34, and connecting the solidscollector cyclone 34 with conduit 28. A cap 38 may be placed over asolids discharge port 40.

The roaster 10 is provided with the usual instrumentation and safetyfeatures, including motor circuits for recirculation fan 32, a blower ingas burner 18, a roaster cylinder drive and cooler fans. Solenoidcircuits are provided for valves and dampers. Timing circuits areprovided for roaster discharge, water spray, cooling time, the pilotflame and filter cleaning cycle. A flame safeguard relay is included andis responsive to both a flame temperature control and a roaster hightemperature limit switch. A temperature recorder monitors thetemperature of the beans and adjusts the flame accordingly.

Operation of a roaster in accordance with the invention may bevisualized in a general way by referring to FIG. 2. It will beappreciated that FIG. 2 is greatly simplified, but the circuitry isconventional and well known in the art, and need not be described hereinin detail.

Motor control circuits 50 are provided for cylinder rotation 50a,recirculation fan motor 50b and burner blower motor 500. A plurality ofsolenoid circuits 52 control, inter alia, purge damper 26, swing gate15, gas regulator 52a and a damper 52b in the collector gas outlet.Flame control circuits 54 provide for ignition, high and low fire andprovides an input 54a to the gas regulator circuit 52a. A thermocouple(TC) senses bean temperature. A second thermocouple senses heat input,and control 55 regulates the flame via 55a.

The damper 26 is set to purge on start-up so that all unburned gases areremoved before ignition. During roasting, the damper is set to permitrecirculation of gases to meet the requirements of the circulating fan,excess gases escaping through the vent pipe 30. At the end of roasting,the damper is set to discharge all effluent during the spray period. Thedamper returns to circulate position when gas is turned on at start ofthe next cycle. The damper is on circulate during the entire clean-outperiod.

A roast cycle timer 56 provides an input for the circuitry controllingswing gate 15.

All of the foregoing is deemed to be more or less standard equipment. Toeffect automatic or semiautomatic operation of the cleaning cycle,according to the invention, additional circuitry is required.

A clean-out cycle timer 58 is required. The frequency of clean-out willvary with operating conditions and the type of bean being treated.However, a daily operation of the cycle has been found to besatisfactory where the roaster is in continuous use. This timer merelyflashes a warning light to the operator that the roaster is due forclean-out. Alternatively, timer 58 can start clean-out directly, asshown at 58a.

Normally, the roaster is operated automatically, i.e., the roasterdischarge timer controls discharging and charging of the machine, andkeeps it continually on stream. When the clean-out cycle timer 58indicates that clean-out is due, which will ordinarily occur during aroasting cycle, operation is first switched from automatic to manual.This will allow the roaster to finish the cycle and discharge theroasted beans, but prevents the roaster swing gate from setting thetrigger to load an- I other batch to the roaster.

When the roaster is discharged, the roaster discharge timer is notreset, because operation is on manual, the recirculation fan stops, anda bleed valve on the gas regulator is energized. The clean-out cycle maynow commence. Equipment therefor includes a clean-out timer, switches,panel indicators and circuitry for overriding certain of the normaloperating controls, as described below with reference to FIG. 3.

A key-operated start switch 60 energizes clean-out relay 62 and lightspanel indicator lamp 64, contacts 66 and 68 being closed at this point.Line R closes contact 70 to hold relay 62 in position. Normally, at thecompletion of each roast, the burner goes to low-fire. Line R closes aninterlock and turns off the roasting on" panel light, and rests theflame to high-fire. Line R opens the circuit containing the hightemperature limit switch, preventing the latter from turning off theflame during clean-out. Line R, energizes a relay in the hightemperature limit switch circuit which prevents water sprays from beingactivated after clean-out and before the roaster has cooled down. Line Ropens a contact in the coffee temperature control circuit, thusoverriding this function. Line R closes a contact, restarting clean-outcycle timer 58 (FIG. 2). Line R opens contacts preventing swing gate 15from charging coffee to the roaster, even if the start switch is pressedin error. Line R restarts circulating fan 32. While the roaster isheating, the operator should change the set point on the flametemperature control to 1,000F.

When the proper clean-out temperature is reached, sensor T closes switch72, starting clean-out timer 74. Clean-out proceeds for the prescribedtime period. Some actual tests are described below.

At the end of the cycle, timer 74 energizes relay 76. Line R openscontact 68, de-energizing relay 62, and line R opens a contact in theflame control circuit, shutting down the burner.

De-energizing relay 62 re-sets all functions for normal operation.However, certain functions should not be re-started until the roasterhas cooled to normal temperatures. Since the high-temperature limitswitch will close during clean-out (with no effect), this is made toenergize a relay which prevents actuation of water sprays and the coffeetemperature controller until the roaster cools down and the limit switchopens.

Under normal operation, the flame safeguard relay will commence aroaster purge cycle whenever the burner shuts off; this is obviouslydesired after the clean-out cycle. When the purge is complete the burneris relighted in low-fire, the flame temperature controller set point isre-set to normal, and when the roaster temperature is at a properroasting level, green coffee beans are then charged in the usual manner.

it will be appreciated that the foregoing describes what is essentiallya semiautomatic operation of the clean-out cycle, i.e., the cycle timermerely signals the operator, who initiates the cycle and makes certainadjustments. Those skilled in the instrumentation art will realize thatoperation of the clean-out cycle could be performed entirely manually byproviding manually op erated switches for the various circuits, or itcould be performed entirely automatically by having the cycle timerenergize the start switch, and providing circuitry to take over alladjustments and override the normal functions. Inasmuch as temperaturesin the recirculation system are well above normal operatingtemperatures, and combustion is taking place within the whole roasterinstallation, it is felt that the presence of an operator provides anextra margin of safety, and the semiautomatic system is preferred.

Two commercial roasters were shut down and thoroughly cleaned. Circuitrywas installed on one roaster for semi-automatic clean-out in accordancewith the invention. It was found that in spite of manual cleaning,combustible residues accumulated in presumably inaccessable places andthe first few clean-out cycles had to be very carefully monitored toprevent uncontrolled combustion. These initial runs also disclosed manyholes, open seams and leaky flanges, which had previously been sealedwith residues. After this break-in period, tests were carried out on adaily basis for three days. Clean-out time (burner-on to burner-off) wasvaried in the range of 5 to 15 minutes, and periods of 6 to 10 minuteswere found satisfactory. Total downtime (roaster discharge to roastercharge) was about 10 to 20 minutes depending on time of roaster burnout.Temperatures within the roaster reached 700 to 750F. (sensor T,),off-gas temperature reached 780F. (sensor T suction box temperaturesreached 570F. (sensor T and collector temperatures reached 650 F.(sensor T,,). It will be appreciated that the number of roasts betweenclean-out, the temperature of cleanout and the length of the clean-outcycle are variables which must be determined for each installation.Experience to date indicates, however, that a clean-out every 50 to 70roasts lasting 5 to minutes and wherein the entire roaster :reachestemperatures in the range of about 350 to 750F. is satisfactory.

After the tests referred to above were completed, both roasters wereinspected (the second roaster was operated during the same period as acontrol without any clean-out).

The roaster cylinder of the test unit was clean to bare metal, with -98percent of the perforations open; the control unit had 30-40 percent ofthe perforations plugged. The cylinder housing of the test unit wasclean, whereas the control unit had a one-eighth to one-fourth inch softcoating of ash and other residues. The circulating fan blades of bothunits were clean, but the control unit had a one-fourth inch coating onthe hub. Piping was generally clean in both units. The col lector in thetest unit was very 'clean, whereas the control unit had a soft coatingof residue up to one-half inch thick. The suction box of the test unitwas clean, with some ash noticeable near the roaster end; the sides ofthe control units suction box had a soft coating, and there was somechaff accumulation.

In summary, the test roaster operated for 16 hours with a total downtimeof 15 minutes, was clean at the end of the test period, and wasoperating with good efficiency throughout the test. The control unitrequired manual cleaning at the end of the test which, includingcool-down and start-up, takes about 10 hours, and the services of amaintenance man.

In accordance with the invention, the roaster is substantiallycontinuously at least at the roasting temperature, and is periodicallyheated to a somewhat higher temperature for clean-out. The roaster iscooled to room temperature only for extraordinary maintenance such asreplacement of parts. Thus, the thermal cycling of a unit operated inaccordance with the invention is actually less severe than when coolingto room temperature for cleaning. While life tests have not beencompleted, it is believed that roasters operated in accordance with theinvention will last longer than roasters not so operated. Of course, itis necessary to be sure all parts of the installation subjected toclean-out are serviceable at the indicated temperatures; plain carbonsteel construction is satisfactory, inasmuch as this material can beused safely at up to about l,00OF.

Various changes in the details, steps, materials and arrangements ofparts, which have been hereindescribed and illustrated in order toexplain the nature of the invention, can be made by those skilled in theart within the principle and scope of the invention as defined in theappended claims.

What is claimed is:

1. Apparatus for periodically effecting clean-out of a coffee roasterhaving a charge container, burner means and a gas recirculation system,comprising:

first timing means capable of indicating when said roaster is due forclean-out;

means preventing further charging of coffee beans when clean-out isindicated;

means capable of igniting said burner means when said charge containeris empty;

sensing means in said recirculation system for sensing the temperaturethereof;

second timing means responsive to said sensing means, and initiating aclean-out cycle when said charge container reaches a predeterminedtemperature, said second timing means also having means associatedtherewith for shutting off said burner on completion of said cycle; and

means capable of purging combustion gases from said roaster oncompletion of said cycle.

said cycle.

3. The apparatus as claimed in claim 2, and additionally comprisingmeans associated with said second timing means for restoring all normalroaster functions upon completion of said clean-out cycle.

1. Apparatus for periodically effecting clean-out of a coffee roasterhaving a charge container, burner means and a gas recirculation system,comprising: first timing means capable of indicating when said roasteris due for clean-out; means preventing further charging of coffee beanswhen clean-out is indicated; means capable of igniting said burner meanswhen said charge container is empty; sensing means in said recirculationsystem for sensing the temperature thereof; second timing meansresponsive to said sensing means, and initiating a clean-out cycle whensaid charge container reaches a predetermined temperature, said secondtiming means also having means associated therewith for shutting offsaid burner on completion of said cycle; and means capable of purgingcombustion gases from said roaster on completion of said cycle.
 2. Theapparatus as claimed in claim 1, wherein said roaster is provided with atemperature limit switch controlling said burner, and additionallycomprising a clean-out temperature limit switch and means capable ofinactivating said temperature limit switch and activating said clean-outtemperature limit switch during said cycle.
 3. The apparatus as claimedin claim 2, and additionally comprising means associated with saidsecond timing means for restoring all normal roaster functions uponcompletion of said clean-out cycle.